Magnetoresistive playback heads for bit-patterned medium recording applications

This work examines playback characteristics of common magnetoresistive heads applied in magnetic recording systems based on bit-patterned medium. Playback for different head designs is evaluated using the reciprocity principle. Analytical solution for a pointlike reader is used to elucidate the playback resolution limits for a given patterned medium morphology. Various recording system design parameters including recording layer design (thickness, bit geometry, and bit-to-bit spacing), exchange/buffer layer thickness, soft underlayers, and fly height are examined. Differential readers are shown to offer significantly higher spatial resolution, higher signal amplitude, and the weakest dependence on fly-height variations and bit geometry. For example, for a 1 Tb/in² reader design considered, D50 is 1.46 and 2.64 Tb/in² for shielded and differential readers, respectively; differential readers have more than 35% higher playback amplitude than equivalent shielded readers. The loss in playback amplitude can be as high 18% due to bit-corner rounding (lithography imperfections) for shielded readers; differential readers exhibit only a weak dependence on bit-corner rounding (±2%–3%). Pseudodifferential readers with a single-sensor element are shown to offer advantages similar to the advantages of conventional double-sensor differential readers while addressing manufacturability issues.